In measuring the modulation transfer characteristics of various image forming systems, it is often desirable to employ a variable transmittance sinusoidal test pattern. The production of photographic sinusoidal test objects having sinusoidal patterns has been described in various places in the scientific literature, for example, in R. L. Lamberts, "The Production and Use of Variable-Transmittance Sinusoidal Test Objects," Applied Optics, 1963, Vol. 2, No. 3, pp 273-276, the disclosure of which is incorporated herein by reference.
As described in the Lamberts paper, approximate linearity of the transmittance exposure relationship can be obtained by using a photographic negative material that is printed onto a positive photographic material, the gammas (contrasts) of the films being adjusted to give an overall gamma of negative unity (-1.0). In such instances, there is a linear relationship between the transmittance of the positive material and the exposure received by the negative material. Thus, when a negative film is exposed with a sinusoidal distribution of light and printed on a positive film, the transmittance of the print will also be approximately sinusoidal. Methods known in the art, however, for producing sinusoidal test objects are often limited as to the range over which good linearity can be obtained. A method for making test objects having a wide range of modulation linearity without unacceptably high harmonic distortion is needed. This need is met by the method of the present invention.